Nanostructured thin films for solid oxide fuel cells

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Title: Nanostructured thin films for solid oxide fuel cells
Author: Yoon, Jongsik
Abstract: The goals of this work were to synthesize high performance perovskite based thin film solid oxide fuel cell (TF -SOFC ) cathodes by pulsed laser deposition (PLD ) , to study the structural , electrical and electrochemical properties of these cathodes and to establish structure -property relations for these cathodes in order to further improve their properties and design new structures . Nanostructured cathode thin films with vertically -aligned nanopores (VANP ) were processed using PLD . These VANP structures enhance the oxygen -gas phase diffusivity , thus improve the overall TF -SOFC performance . La0 .5Sr0 .5CoO3 (LSCO ) and La0 .4Sr0 .6Co0 .8Fe0 .2O3 (LSCFO ) were deposited on various substrates (YSZ , Si and pressed Ce0 .9Gd0 .1O1 .95 (CGO ) disks ) . Microstructures and properties of the nanostructured cathodes were characterized by transmission electron microscope (TEM ) , high resolution TEM (HRTEM ) , scanning electron microscope (SEM ) and electrochemical impedance spectroscopy (EIS ) measurements . A thin layer of vertically -aligned nanocomposite (VAN ) structure was deposited in between the CGO electrolyte and the thin film LSCO cathode layer for TF -SOFCs . The VAN structure consists of the electrolyte and the cathode materials in the composition of (CGO ) 0 .5 (LSCO ) 0 .5 . The self -assembled VAN nanostructures contain highly ordered alternating vertical columns formed through a one -step thin film deposition using a PLD technique . These VAN structures significantly increase the interface area between the electrolyte and the cathode as well as the area of active triple phase boundary (TPB ) , thus improving the overall TF -SOFC performance at low temperatures , as low as 400oC , demonstrated by EIS measurements . In addition , the binary VAN interlayer could act as the transition layer that improves the adhesion and relieves the thermal stress and lattice strain between the cathode and the electrolyte . The microstructural properties and growth mechanisms of CGO thin film prepared by PLD technique were investigated . Thin film CGO electrolytes with different grain sizes and crystal structures were prepared on single crystal YSZ substrates under different deposition conditions . The effect of the deposition conditions such as substrate temperature and laser ablation energy on the microstructural properties of these films are examined using XRD , TEM , SEM , and optical microscope . CGO thin film deposited above 500 ?C starts to show epitaxial growth on YSZ substrates . The present study suggests that substrate temperature significantly influences the microstructure of the films especially film grain size .
URI: http : / /hdl .handle .net /1969 .1 /ETD -TAMU -3164
Date: 2009-05-15

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Nanostructured thin films for solid oxide fuel cells. Available electronically from http : / /hdl .handle .net /1969 .1 /ETD -TAMU -3164 .

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